feat(telemetry): trace context compaction

agent/agent.go

@@ -238,6 +238,19 @@ func getAuthorForEvent(ctx Context, event *session.Event) string {
 	return ctx.Agent().Name()
 }
 
+// eventActionsFrom returns the actions a callback accumulated, less the fields
+// that are the framework's to write rather than a callback's.
+//
+// A callback is handed the live [session.EventActions] so it can request state
+// deltas, escalation and transfers, and the struct is then copied wholesale onto
+// the persisted event. Anything on it that changes how later prompts are built
+// has to be filtered out here, or the callback gets to set it.
+func eventActionsFrom(actions *session.EventActions) session.EventActions {
+	out := *actions
+	out.Compaction = nil
+	return out
+}
+
 // runBeforeAgentCallbacks checks if any beforeAgentCallback returns non-nil content
 // then it skips agent run and returns callback result.
 func runBeforeAgentCallbacks(ctx InvocationContext) (*session.Event, error) {
@@ -259,7 +272,7 @@ func runBeforeAgentCallbacks(ctx InvocationContext) (*session.Event, error) {
 			}
 			event.Author = agent.Name()
 			event.Branch = ctx.Branch()
-			event.Actions = *actions
+			event.Actions = eventActionsFrom(actions)
 			ctx.EndInvocation()
 			return event, nil
 		}
@@ -280,7 +293,7 @@ func runBeforeAgentCallbacks(ctx InvocationContext) (*session.Event, error) {
 		}
 		event.Author = agent.Name()
 		event.Branch = ctx.Branch()
-		event.Actions = *actions
+		event.Actions = eventActionsFrom(actions)
 		ctx.EndInvocation()
 		return event, nil
 	}
@@ -290,7 +303,7 @@ func runBeforeAgentCallbacks(ctx InvocationContext) (*session.Event, error) {
 		event := session.NewEvent(ctx, ctx.InvocationID())
 		event.Author = agent.Name()
 		event.Branch = ctx.Branch()
-		event.Actions = *actions
+		event.Actions = eventActionsFrom(actions)
 		return event, nil
 	}
 
@@ -318,7 +331,7 @@ func runAfterAgentCallbacks(ctx InvocationContext) (*session.Event, error) {
 			}
 			event.Author = agent.Name()
 			event.Branch = ctx.Branch()
-			event.Actions = *actions
+			event.Actions = eventActionsFrom(actions)
 			return event, nil
 		}
 	}
@@ -338,7 +351,7 @@ func runAfterAgentCallbacks(ctx InvocationContext) (*session.Event, error) {
 		}
 		event.Author = agent.Name()
 		event.Branch = ctx.Branch()
-		event.Actions = *actions
+		event.Actions = eventActionsFrom(actions)
 		// TODO set context invocation ended
 		// ctx.invocationEnded = true
 		return event, nil
@@ -349,7 +362,7 @@ func runAfterAgentCallbacks(ctx InvocationContext) (*session.Event, error) {
 		event := session.NewEvent(ctx, ctx.InvocationID())
 		event.Author = agent.Name()
 		event.Branch = ctx.Branch()
-		event.Actions = *actions
+		event.Actions = eventActionsFrom(actions)
 		return event, nil
 	}
 	return nil, nil

internal/agent/compactionctx/compactionctx.go

@@ -0,0 +1,69 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package compactionctx carries the context-compaction runtime from the runner
+// down to the request processors that need it.
+//
+// Those processors need the compaction config, and in one case the session
+// service, and [agent.InvocationContext] exposes neither. Adding them to that
+// interface would break every external implementation of it, so the runtime
+// rides on the context.Context instead, the same way parentmap, runconfig and
+// plugininternal already do.
+package compactionctx
+
+import (
+	"context"
+
+	"google.golang.org/adk/v2/session"
+	"google.golang.org/adk/v2/session/compaction"
+)
+
+// Runtime is everything compaction needs that the invocation context does not
+// already provide.
+type Runtime struct {
+	// Config is the resolved compaction config, with its summarizer filled in.
+	Config *compaction.Config
+	// SessionService persists the summary events the compactor produces.
+	SessionService session.Service
+}
+
+// Configured reports whether compaction is enabled for this run.
+//
+// Prompt assembly gates on this rather than simply honouring any compaction
+// record it finds. A record instructs the prompt builder to drop a range of
+// history and substitute content in its place, so acting on one that this
+// runner did not ask for would turn a stored field into an erase-and-inject
+// primitive, available even to an application that never enabled compaction.
+func (rt *Runtime) Configured() bool {
+	return rt != nil && rt.Config != nil
+}
+
+// ToContext returns a context carrying rt.
+func ToContext(ctx context.Context, rt *Runtime) context.Context {
+	return context.WithValue(ctx, runtimeCtxKey, rt)
+}
+
+// FromContext returns the [Runtime] carried by ctx, or nil when compaction is
+// not configured.
+func FromContext(ctx context.Context) *Runtime {
+	rt, ok := ctx.Value(runtimeCtxKey).(*Runtime)
+	if !ok {
+		return nil
+	}
+	return rt
+}
+
+type ctxKey int
+
+const runtimeCtxKey ctxKey = 0